I have a one-terabyte Time Capsule (third generation, 802.11n) that's served me well since I got it a few years ago (I don't remember exactly when). I use it mostly as the primary router in my home network, and also for backups (though I haven't run one since May or so). It also holds some TV shows and other things that won't fit on my Mac's hard drive. I haven't had any problems with it, and it's always been nice and fast for my purposes.

A few days ago, though, I decided to move everything I had there (not including the backups) to an encrypted sparsebundle, and I noticed that, while my network seemed as fast as it usually was, file transfers to the Time Capsule's internal drive were slower, and stalled often. Usually when there's disk activity, if I put my ear by the Time Capsule, I can hear a humming and lots of soft clicks (which I assume are the disks spinning and the read|write head moving). This is normal as far as I know; it's happened since day one whenever I do anything with the drive. Now, I don't hear the clicks when copies stall, though the humming continues as long as I'm trying to do anything.

Various programs have stalled on me trying to copy to the disk (cp, scp, dd, etc), and in the case of the Finder, it will freeze entirely while the operation is stalled. Programs with stalled disk operations show up as U (in uninterruptible wait) in ps, and if I try to use ^C, E appears too (trying to exit).

What's the likely cause of this? Is it just that the Time Capsule is getting old and I'll have to buy a new one soon? Is there anything I can do to help, or a possible software-based cause?